This invention relates to an organopolysiloxane composition for bonding to magnesium alloys which is cured at room temperature into a cured product having an excellent bonding property to magnesium alloys.
In recent years, magnesium alloys, typically AZ-31, AZ-91 and the like, have distinct features of lightweight and high strength, a good corrosion resistance, good designing properties and good recycling properties, and have been frequently used in information electronic devices such as mobile phones, digital video recorders, digital cameras, liquid crystal projectors, plasma displays, personal computers, MD players, DVD recorders and the like, and also in transport machine parts such as electric components, vehicle oil pans, intake manifolds, lock housing parts, steering upper brackets, steering wheels and the like. Organopolysiloxane compositions for bonding to magnesium alloys exhibiting good self-adhesiveness to these members are now needed.
However, magnesium alloys are adherends which are difficult to bond. Eventually, chemical conversion treatment is essential for bonding. Sealing members or adhesives exhibiting good self-adhesiveness without the conversion treatment have been never studied. More particularly, only several types of organopolysiloxane compositions having self-adhesiveness to magnesium alloys have been proposed up to now. JP-A 2003-535152 discloses a composition comprising a curable silicone and an amino group-containing silane adhesion promoter serving as a filler. JP-A 2002-309219 has proposed a composition comprising a silicone oil and a curing agent composed of an inorganic compound containing a metal element whose tendency of ionization is smaller than that of magnesium. However, the former composition is not satisfactory with respect to the effectiveness of the amino group-containing silane adhesion promoters such as γ-aminopropyltrialkoxysilane, trialkoxypropylethylenediamine and the like. With the latter, limitation is placed on the type of filler used, thus lacking in the freedom for material designing.